Group 24 cells

[Burgerman]

Its connected to your main subD charge connector, it needs the cell taps, and so has power.

[jefferso]

Went back to 30 amps charging. It put back 22 Ah. I'll try 20 amps and changing the termination current soon.

[jefferso]

Charged at 20 amps yesterday but had to stop before it finished. It had put about 81 Ah back in and gotten close to 3.4v per cell.
Today I finished the charge at 20 amps and it put about 23Ah in.

[shirley_hkg]

I'd go for 25 amp recharge rate for 160Ah pack.

[Burgerman]

You can charge partly or add say 50Ah and use the chair a few times without bothering with a full charge too. Its not required to complete a full charge every time. Lithium doesent care. As long as it stays generally in balance. And that pack looks like it does well now. I charge at lower amps when no hurry. And max power and 40A if I am in a hurry... Also depends how discharged of course and your plans! You will learn what you need and how fast your usage and oxygen concentrator use power.

After you put 100Ah back, that means you still had equivelent to a full set of lead batteries and a third remaining.

[Superchunk]

So, update on my side, I tested it out in my invacare tdx sp2 chair (it takes 22NF batteries so had to take the battery tray out ). And it worked perfectly! The only thing I'm still unsure about is how to wire the circuit breaker in the permobil, positive cell 8 and 24v positive or something else?

[shirley_hkg]

Right.
One end of the braker goes to the +ve terminal of battery , and the other connects the +ve lug of the power module with nut & bolt.

[jefferso]

So, update on my side, I tested it out in my invacare tdx sp2 chair (it takes 22NF batteries so had to take the battery tray out ). And it worked perfectly! The only thing I'm still unsure about is how to wire the circuit breaker in the permobil, positive cell 8 and 24v positive or something else?

Here's a drawing I made to illustrate in my mind how I did the breaker on my Permobil F5 VS. I used an M6 nut and bolt (M6 x 10mm) from ebay to connect the red and grey cable on the left side of the battery tray.
https://www.ebay.co.uk/itm/155249347541

Then the grey cable connected to the red cable on the left side which goes to the chair is connected to the breaker and the other grey cable from the breaker to the positive of cell 8 and the black cable on the right side which goes to the chair is connected to the negative of cell 1.

The charging cable is connected independently to negative of cell 1 and positive of cell 8.
Currently with my setup the breaker is for the chair only. I can turn the breaker off and still charge the chair. I'll probably add a fuse to the charging cable because as it is there's no over-current protection when charging.

This isn't the only way to do it. You could also wire it so the breaker is in between the two halves of the pack. You could remove the interconnect between positive of cell 4 and negative of cell 5 and connect the grey cables from the breaker to those terminals. That would give protection to the chair and charging. But I think Burgerman says it might make some strange values for those cells during charging?

[Burgerman]

I will be using a 150A fuse at the pos. Maybe a few 200A just in case ones beween cells. As cell interconnects. No breakers I dont like them. Not reliable.

[jefferso]

I did another full charge. 33Ah this time for a day and a half.
I did this one at 25 amps. One interesting thing is that the PL8's fan came on after about 15 minutes of 25amp charging then stayed on until it went below 25 amps. When I charged at 20 amps, the fan would come on occasionally for about 5 minutes at a time then stay off for 20 minutes or so. So if I want a quieter charge maybe around 18 amps would allow a full charge without the fan coming on. I imagine it depends on how hot the room is too.
The latest generation ZXD has been quiet all the time.

[jefferso]

I wonder if 8 of these 100 Ah could fit in a Group 24 space on their sides:

https://www.docanpower.com/index.php?ro ... arch=100ah

100 Ah
(Width)：160
(Height)：118.5
(Thickness)：50

4 x 50mm thickness = 200mm height, + 5 x 1mm insulation, 205mm (MK Gel = 209mm high)

118.5 mm x 2 = 237mm (MK Gel = 259mm length) would leave 22mm, 11mm for each set of terminals and connectors. Seems like not enough space.

160mm height, on its side, becomes width (MK Gel = 173mm width)

[Burgerman]

Cant do that sideways thing in my head.

But I am 36 days into my 45 to 60 day wait for the 230Ah (245Ah actual) cells...

I have absolutely zero patience. Even the word patience is too long, I am frustrated just saying that oh so long word. I also dont and cannot que, or watch an ad ever...

But am perfectly happy polishing power tools, ordering tools in order of type, size, length, etc. My ex thinks am mad. I think all women and most people are.

[c500user]

I wonder if 8 of these 100 Ah could fit in a Group 24 space on their sides:

https://www.docanpower.com/index.php?ro ... arch=100ah

100 Ah
(Width)：160
(Height)：118.5
(Thickness)：50

4 x 50mm thickness = 200mm height, + 5 x 1mm insulation, 205mm (MK Gel = 209mm high)

118.5 mm x 2 = 237mm (MK Gel = 259mm length) would leave 22mm, 11mm for each set of terminals and connectors. Seems like not enough space.

160mm height, on its side, becomes width (MK Gel = 173mm width)

Although the Eve LF100 are rated at 1C continuous discharge (3C max), I would try to go for a bit more, if you can.
I have a Permobil C500 that only just has enough space for the MK Gels, so know your dilemma. I ended up buying 16x80Ah cells that are lower (170mm off the top of my head) and I should be able to squeeze 8 into the space of 1 MK Gel. Total capacity will then be 160Ah.
I have had them for a while, just was uncomfortable putting them in without good protection, and need to design a simple 3D printed box and have it made by one of the fabrication houses in China. Too many projects means it will be waiting a bit longer.

I don't know where you are located, and can't vouch for this seller, but these are the ones I mean:
https://www.evcomponents.com/eve-3-2v-80ah-prismatic-lifepo4-cell.html

[Burgerman]

I agree. Be wary of C rate claims. All are exadurated as it sells more cells. In any case consider this. These great 2000 to 10,000 cycle claims that are made, are actually true but only when tested at 0.2 or 0.25C discharge rates. See spects. Higher rates are possible too but it murders the cycle life. So they dont advertise this.

So this is why you should always maximise capacity. The lower the average and peak C rate discharge the better. Regardless of the max C rate they can survive without swelling or overheating. This is why the drop in lead brick options dont make any sense. Unless you do everything possible to either use high C rate cells (3C continuous 10C peak for e.g) then you will not get close to the rated cycle life. You neet lots of headroom.

Likewise, just like lead the more deeply you discharge them on a daily basis the faster they will die. So again bigger is better. And of course even if you were to get the same cyce life, a big battery means you can charge less often. Maybe 2 or 3 times less often than the lead brick drop ins or 100Ah battery. So your cycle life lasts 2 0r 3x longer in years even with similar cycle numbers!
AND if you only have 100Ah to start with, then say a 33% capacity loss leaves just 66Ah. Same as a set of lead bricks.
A 33% loss of capacity on a 230Ah pack, means you still have over 154Ah left and still have 3.5x the range of lead! And this will never happen on a big pack.

Bigger is better! There comes a point where this no longer makes sense. Diminishing returns. In a chair thats likely around 200 to 300Ah for most people. At this point you have endless daily range, and a battery that gets a very easy life and so should out live the chair or the user probably! Not alot of benefit going bigger for most people.

[jefferso]

I am probably going to replace the interconnect which had the insulation melt sometime soon. I looked at the spec sheet for the 160Ah cells but couldn't find a recommended torque setting to tighten the nuts on the cell posts. The 230Ah cell spec sheet has "Welding Parameter of Al Busbar, Max Torque Force on Poles, 6 N ·m, Max torsion, non-loosen."
I got a 5 - 25 Nm torque wrench. Is 5 Nm a sensible setting to tighten them?

[shirley_hkg]

youtu.be/uaebFJQchao

It's pretty strong actually .

[Burgerman]

6Nm is about 4.4 lb-ft which is quite a lot for a small 6mm bolt.

Same as using a 300mm or 12 inch long bar, or a long ratchet? and hanging 2kg bottle of coke from the end of the handle. A DIY torque wrench!

When you have been building cars, bikes, and hobby stuff for a lifetime you dont need a torque wrench or figures, you naturally have a feel for how much force to use based on thread size, pitch, materials its made from (how hard) etc. And its around the same as above. If thats you then you wont worry about settings and torque wrenches unless you are building a race engine! You will just use "feel" and experience...

If thats not you, By all means buy a small cheap torque wrench! Set it to say 3.8lb foot, or 4 lb-ft its a unlubricated thread (always use a tiny bit of grease on stainless threads though) and that leaves some headroom for safety. Assemble with all flat surfaces cleaned with some fine abrasive or scotchbrite cloth to b sure its virgin metal, not oxides or finger grease etc. And a quick squirt of switch cleaner! Such as De-oxit. Theres many brands. They include a deoxidiser, and a wetting agent so good ultra low resistance is achieved. And a oily coating remains that prevents future oxidation.

Use a flat washer before the nut, dont use flanged nuts. Use a nyloc with a tiny bit of lubricant. And if no nyloc, a small dab of blue loctite on a plain nut or even some paint to ensure it doesent get loosened. HEAT a little before removal if you have to do so as this frees the loctite. SOLDER all balance and main connectors with flux, and clean remains of flux off well, dont rely on crimp connectors alone. Thats asking for trouble. Especially as theres so many. Dont use bare copper terminals, or bus bars either. Use tinned, nickel, zinc etc plated ones.

[jefferso]

The pack has two ring terminals, one thick and one thin for about half the terminals (interconnect and balance wire) and a single thick (interconnect) for the others. Does the order those go on the bolt matter? Should it be interconnect ring, then balance wire ring, then washer, then nut?

[Burgerman]

Yep.

[jefferso]

You can increase termination current a little. By around 25%. So if its set to say 200mA for e.g set to 250. Keep doing that until it ends after around 15 to 20 mins after it is at CV balanced. Its pretty good already. Manual fine tune! Its not critical. But why not.

Right now the termination current is 500mA. So I could go up to 625mA and see how quickly it finishes?

[Burgerman]

Yes.

You could set a CV time limit. But it doesent respect the other settings (I think). So if the balance isnt achieved for e.g then it will end regardless. So best to use that as a safeguard and set it to say 8 hours. And make sure the thing terminates when it reaches the current choosen instead. Or at least first!

And if you set a time limit then an initially built pack for e.g will never have time to balance itself on a first charge.

[jefferso]

It's been a couple of weeks since I did a full charge of the pack. I often skip charging on weekends and one or two other days in the week and only add back part of what I've used. Maybe recharge to around 80% full. This is the lowest it's gotten in a while. Added back 84171 mAh at 30 amps. Cell 7 is occasionally higher during the charge, sometimes .003 v higher, but it varies and is often exactly the same as the others.

It sure is nice not having to worry about the charge every day. I had to meet someone at the Tate Modern museum. Normally I'd have to consider whether I should take a train as close as I could get, say Blackfriars station, the closest accessible station on the Circle Line, then I might do lots of estimates of battery charge in my head, think about what I might do later, how much battery I'll need, how long I used my ventilator since last full charge, decide whether to take a bus the rest of the way to save battery so I don't go down much under 50%. But now I don't even think about battery as a limiting factor. If it's nice weather, it's no problem to roll 20 minutes or more and not have to wait for a bus or deal with a pram in the wheelchair space. Then later I can roll to Tower Hill station, the closest accessible station in the other direction on the Circle Line, another 30 minutes away.

[Burgerman]

Looks perfect.
Graph shows 3.550V
BUT FOR SOME ODD REASON THE Text on the top left shows 3.67V which is too high and looks incorrect?


0.003 of a volt is a microscopic difference of 3 one thousandths of 1 volt!

I doubt that the charger is that accurate anyway.
A different PL8 may never show that. Or show a different cell thats 0.003V out.

Its good losing that range anxiety that we all have built in. But the lead and battery meter training takes a long while to wear off. Most people think they dont have it. Because subconciously they are programmed to lower expectations. The chair trained them
THEN once you have silly range you lose that and naturally do more.

I could drive my salsa, in spring when I fit ts new 244Ah lithium batt, for approx 14 hours solid at full speed without stopping. At its current Ah per mile normal consumption rate. Thats 86 miles @ 6.2mph. And still have a safe 14+ miles in reserve. (Same as a full set of lead bricks!) remaining. Realistically thats just never going to happen.

[jefferso]

It's been about two weeks since I did a full charge. I've just been doing a charge every other day or so for an hour or two to keep up with battery use.

Here's today's full charge. I think it got to the set point and stopped then was drifting down very slightly over a few minutes. Looks like it was just over half full when I started the charge. I'm still so pleased with having 160ah and the ability to recharge quickly,

[Burgerman]

Looking perfect.

[jefferso]

Yesterday I was in a restaurant and I suddenly smelled a burnt smell which reminded me of when I had a lose connection between cells and the insulation on an interconnect cable melted:

https://www.wheelchairdriver.com/board/ ... 40#p205015

I think the smell might have just been someone blowing out a candle in the restaurant, but I kept thinking about it so got the battery out to double check today. All interconnects look good. None look melted. My cheap torque wrench starts at 55 lb - ft, so I set it to that and all nuts are still at least that tight. Kind of a pain to do it but just wanted to be sure before doing another charge.

[Burgerman]

Better safe than sorry. But you have 100 times better chance of success than someone that trusted some random to build a battery! That almost always ends badly!

Did you manage to go far enough to make a dent in the range yet?

[jefferso]

I'm barely scratching the surface. Other than the convenience of not having to charge for three or four days at a time.
I went 7.5km (4.7mi) the other day without a second thought, and powered my ventilator from the chair without having to estimate how long I could safely run it before it made a dent in the battery. Hadn't charged since Saturday and just put 80 Ah back in this morning.

[Burgerman]

That would have been 2 safe full lead battery discharges. And half your lithium battery. And light use. So will last a lifetime all being well.

Once you tried this for a bit and get used to not being tied to a battery meter you will tend to venture further and never think about batteries. Especially so if you need a vent.

[shirley_hkg]

Never going back, once tasted the honey drew.